Though the terrorists came from at least eight countries, all shared one overriding belief — that America is waging war on Muslims.

One well-known cleric from Jordan, Omar Yousef Jumah, was killed in September and eulogized in a video posted on the Internet only days ago.

In an exclusive interview with NBC News, the cleric's parents say they didn't know he'd even gone to Iraq until they learned of his death.

"Omar sacrificed his kids, his wife, his youth to be a martyr," says his mother. "I'm very proud of him."

Jumah and his family celebrated the 9/11 attacks.

Omar Yousef Jumah’s father says they were all "very happy to see victory for the Muslims."

"America has attacked us in our homes, so it is good that America is attacked in its core," echoes Jumah's mother.

His parents say Omar was secretive and spent his time teaching Islam. They say he told them he was going to Saudi Arabia last year.

In fact, he went to Iraq, where he attracted the attention of Iraq's most-wanted terrorist, Abu Musab al-Zarqawi, who called Jumah, "my soulmate in joy" and said of him, "as my shadow never left me he was a true friend."

The Zarqawi video also suggests Omar played a role in the beheading of American Nick Berg.

Omar's parents say they didn't know he was involved with Zarqawi, just that he died fighting Americans.

"We support what Omar did in Iraq because it is a duty," says Jumah's father.

Families of most of the terrorists expressed pride and support. But one Saudi father is furious. He blames radical Saudi clerics for his son's death, complaining the clerics manipulate young Saudis, telling them it is their duty to go to Iraq and fight the infidels.

In fact, almost half of the so-called "martyrs" NBC News identified came from Saudi Arabia, as part of a seemingly endless stream of young men — educated, and not — willing to die for the mere chance to kill Americans.